There are small packs that are basically just nylon duffel bags with shoulder straps that roll up to a small size. I used one as a day pack for my last few European trips (I carried it on my chest when my backpack got too full of souvenirs, wine, etc.). However, this would only be suitable if you were carrying it all the time--as Tom says, it's far too fragile to trust to baggage handlers. Whether this would work for what you'd want to carry for a weekend, it's hard to say. It would basically just carry toilet articles, spare socks and a jacket. I can't give you recommendations because I bought mine 22 years ago from a firm that's now out of business.

And Tom is right--I would never, never trust any of my backpacking gear to baggage handlers. For traveling, I used a convertible travel backpack. It has internal stays and a hipbelt so is comfy to carry. The shoulder straps and hibbelt can be zipped behind a panel both for airline travel and to look like a regular suitcase if I want to stay in a hotel instead of a hostel. It is twice as heavy as the pack I use for backpacking! It is an REI house brand bought in 1992. I have used it for all kinds of travel and it still looks as good as new. I have no idea if REI is still making this model.

I still think you'll get better recommendations from a travel site.